Chemical and biological characterization of the galactose binding lectins from Trichosanthes kirilowii root tubers.

Three galactose binding isolectins have been isolated from Trichosanthes kirilowii root tubers. Two of the isolectins, TK-I and TK-II, are similar in many aspects including molecular weight, amino acid composition, NH2-terminal amino acid residue, blood group and carbohydrate specificities, immunodiffusion and immunoelectrophoretic behavior, hemagglutinating and insulinomimetic activities, and in possessing subunits with different molecular weights. Compared to TK-I and TK-II, lectin TK-III has a larger molecular weight, subunits with the same molecular weight, a single and distinctive NH2-terminal amino acid residue, a different isoelectric point and lower hemagglutinating activity. The three lectins share common antigenic determinants in their structures. beta-Linked terminal oligosaccharides containing D-galactose inhibit hemagglutination induced by the lectins with a higher potency than alpha-linked oligosaccharides. The lectins are non-mitogenic and did not inhibit the concanavalin-A induced mitogenic response of lymphocytes.